Patchwork D8958: hg-core: Add a limited readonly revlog implementation

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Submitter phabricator
Date Aug. 26, 2020, 1:25 p.m.
Message ID <differential-rev-PHID-DREV-hvlonq22luf4lhqxzksd-req@mercurial-scm.org>
Download mbox | patch
Permalink /patch/47061/
State Superseded
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phabricator - Aug. 26, 2020, 1:25 p.m.
acezar created this revision.
Herald added a reviewer: hg-reviewers.
Herald added a subscriber: mercurial-patches.

REVISION SUMMARY
  Only covers the needs of the upcoming `rhg debugdata` command.

REPOSITORY
  rHG Mercurial

BRANCH
  default

REVISION DETAIL
  https://phab.mercurial-scm.org/D8958

AFFECTED FILES
  rust/Cargo.lock
  rust/hg-core/Cargo.toml
  rust/hg-core/src/revlog.rs
  rust/hg-core/src/revlog/index.rs
  rust/hg-core/src/revlog/patch.rs
  rust/hg-core/src/revlog/revlog.rs

CHANGE DETAILS




To: acezar, #hg-reviewers
Cc: mercurial-patches, mercurial-devel

Patch

diff --git a/rust/hg-core/src/revlog/revlog.rs b/rust/hg-core/src/revlog/revlog.rs
new file mode 100644
--- /dev/null
+++ b/rust/hg-core/src/revlog/revlog.rs
@@ -0,0 +1,338 @@ 
+use std::borrow::Cow;
+use std::fs::File;
+use std::io::Read;
+use std::ops::Deref;
+use std::path::Path;
+
+use byteorder::{BigEndian, ByteOrder};
+use flate2::read::ZlibDecoder;
+use log;
+use memmap::MmapOptions;
+use micro_timer::timed;
+use zstd;
+
+use super::index::Index;
+use super::patch;
+use crate::revlog::Revision;
+
+/// Read only implementation of revlog.
+pub struct Revlog {
+    /// When index and data are not interleaved: bytes of the revlog index.
+    /// When index and data are interleaved: bytes of the revlog index and
+    /// data.
+    index_bytes: Box<dyn Deref<Target = [u8]> + Send>,
+    /// When index and data are not interleaved: bytes of the revlog data
+    data_bytes: Option<Box<dyn Deref<Target = [u8]> + Send>>,
+}
+
+impl Revlog {
+    /// Open a revlog index file.
+    ///
+    /// It will also open the associated data file if index and data are not
+    /// interleaved.
+    #[timed]
+    pub fn open(index_path: &Path) -> Result<Self, std::io::Error> {
+        let index_file = File::open(index_path)?;
+        let index_mmap = unsafe { MmapOptions::new().map(&index_file) }?;
+        let is_inline = is_inline(index_mmap.deref());
+        assert_eq!(
+            version(index_mmap.deref()),
+            1,
+            "Only revlog v1 is supported at this moment",
+        );
+
+        let index_bytes = Box::new(index_mmap);
+
+        // TODO load data only when needed //
+        // type annotation required
+        // won't recognize Mmap as Deref<Target = [u8]>
+        let data_bytes: Option<Box<dyn Deref<Target = [u8]> + Send>> =
+            if is_inline {
+                None
+            } else {
+                let data_path = index_path.with_extension("d");
+                let data_file = File::open(&data_path)?;
+                let data_mmap = unsafe { MmapOptions::new().map(&data_file) }?;
+                Some(Box::new(data_mmap))
+            };
+
+        Ok(Revlog {
+            index_bytes,
+            data_bytes,
+        })
+    }
+
+    /// Return the full data associated to a revision.
+    ///
+    /// All entries required to build the final data out of deltas will be
+    /// retrieved as needed, and the deltas will be applied to the inital
+    /// snapshot to rebuild the final data.
+    #[timed]
+    pub fn get_rev_data(&self, rev: Revision) -> Option<Vec<u8>> {
+        // Todo return -> Cow
+        let mut entry = self.get_entry(rev)?;
+        let mut delta_chain = vec![];
+        while let Some(base_rev) = entry.base_rev {
+            delta_chain.push(entry);
+            entry = self.get_entry(base_rev).unwrap_or_else(|| {
+                panic!("base rev should exist: {:?}", base_rev)
+            });
+        }
+
+        if delta_chain.is_empty() {
+            Some(entry.data().into())
+        } else {
+            Some(self.build_data_from_deltas(entry, delta_chain))
+        }
+    }
+
+    /// Build the full data of a revision out its snapshot
+    /// and its deltas.
+    #[timed]
+    fn build_data_from_deltas(
+        &self,
+        snapshot: RevlogEntry,
+        mut deltas: Vec<RevlogEntry>,
+    ) -> Vec<u8> {
+        deltas.reverse();
+        let snapshot = snapshot.data();
+        let deltas: Vec<_> = deltas.iter().map(RevlogEntry::data).collect();
+        let patches: Vec<_> =
+            deltas.iter().map(|d| patch::PatchList::new(d)).collect();
+        let patch = patch::fold_patch_lists(&patches);
+        patch.apply(&snapshot)
+    }
+
+    /// Return the revlog index.
+    fn index(&self) -> Index {
+        let is_inline = self.data_bytes.is_none();
+        Index::new(&self.index_bytes, is_inline)
+    }
+
+    /// Return the revlog data.
+    fn data(&self) -> &[u8] {
+        match self.data_bytes {
+            Some(ref data_bytes) => &data_bytes,
+            None => &self.index_bytes,
+        }
+    }
+
+    /// Get an entry of the revlog.
+    fn get_entry(&self, rev: Revision) -> Option<RevlogEntry> {
+        let index = self.index();
+        let index_entry = index.get_entry(rev)?;
+        let start = index_entry.offset();
+        let end = start + index_entry.compressed_len();
+        let entry = RevlogEntry {
+            rev,
+            bytes: &self.data()[start..end],
+            compressed_len: index_entry.compressed_len(),
+            uncompressed_len: index_entry.uncompressed_len(),
+            base_rev: if index_entry.base_revision() == rev {
+                None
+            } else {
+                Some(index_entry.base_revision())
+            },
+        };
+        Some(entry)
+    }
+}
+
+/// The revlog entry's bytes and the necessary informations to extract
+/// the entry's data.
+#[derive(Debug)]
+pub struct RevlogEntry<'a> {
+    rev: Revision,
+    bytes: &'a [u8],
+    compressed_len: usize,
+    uncompressed_len: usize,
+    base_rev: Option<Revision>,
+}
+
+impl<'a> RevlogEntry<'a> {
+    /// Extract the data contained in the entry.
+    pub fn data(&self) -> Cow<'_, [u8]> {
+        if self.bytes.is_empty() {
+            return Cow::Borrowed(&[]);
+        }
+        match self.bytes[0] {
+            // Revision data is the entirety of the entry, including this
+            // header.
+            b'\0' => Cow::Borrowed(self.bytes),
+            // Raw revision data follows.
+            b'u' => Cow::Borrowed(&self.bytes[1..]),
+            // zlib (RFC 1950) data.
+            b'x' => Cow::Owned(self.uncompressed_zlib_data()),
+            // zstd data.
+            b'\x28' => Cow::Owned(self.uncompressed_zst_data()),
+            format_type => panic!("unknown format type: {:?}", format_type),
+        }
+    }
+
+    fn uncompressed_zlib_data(&self) -> Vec<u8> {
+        let mut decoder = ZlibDecoder::new(self.bytes);
+        if self.is_delta() {
+            let mut buf = Vec::with_capacity(self.compressed_len);
+            decoder.read_to_end(&mut buf).expect("corrupted zlib data");
+            buf
+        } else {
+            let mut buf = vec![0; self.uncompressed_len];
+            decoder.read_exact(&mut buf).expect("corrupted zlib data");
+            buf
+        }
+    }
+
+    fn uncompressed_zst_data(&self) -> Vec<u8> {
+        if self.is_delta() {
+            let mut buf = Vec::with_capacity(self.compressed_len);
+            zstd::stream::copy_decode(self.bytes, &mut buf)
+                .expect("corrupted zstd data");
+            buf
+        } else {
+            let mut buf = vec![0; self.uncompressed_len];
+            let len = zstd::block::decompress_to_buffer(self.bytes, &mut buf)
+                .expect("corrupted zstd data");
+            if len != self.uncompressed_len {
+                panic!("corrupted zstd data (bad length)")
+            };
+            buf
+        }
+    }
+
+    /// Tell if the entry is a snapshot or a delta
+    /// (influences on decompression).
+    fn is_delta(&self) -> bool {
+        self.base_rev.is_some()
+    }
+}
+
+/// Value of the inline flag.
+pub fn is_inline(index_bytes: &[u8]) -> bool {
+    match &index_bytes[0..=1] {
+        [0, 0] | [0, 2] => false,
+        _ => true,
+    }
+}
+
+/// Format version of the revlog.
+pub fn version(index_bytes: &[u8]) -> u16 {
+    BigEndian::read_u16(&index_bytes[2..=3])
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    use super::super::index::IndexEntryBuilder;
+
+    #[cfg(test)]
+    pub struct RevlogBuilder {
+        version: u16,
+        is_general_delta: bool,
+        is_inline: bool,
+        offset: usize,
+        index: Vec<Vec<u8>>,
+        data: Vec<Vec<u8>>,
+    }
+
+    #[cfg(test)]
+    impl RevlogBuilder {
+        pub fn new() -> Self {
+            Self {
+                version: 2,
+                is_inline: false,
+                is_general_delta: true,
+                offset: 0,
+                index: vec![],
+                data: vec![],
+            }
+        }
+
+        pub fn with_inline(&mut self, value: bool) -> &mut Self {
+            self.is_inline = value;
+            self
+        }
+
+        pub fn with_general_delta(&mut self, value: bool) -> &mut Self {
+            self.is_general_delta = value;
+            self
+        }
+
+        pub fn with_version(&mut self, value: u16) -> &mut Self {
+            self.version = value;
+            self
+        }
+
+        pub fn push(
+            &mut self,
+            mut index: IndexEntryBuilder,
+            data: Vec<u8>,
+        ) -> &mut Self {
+            if self.index.is_empty() {
+                index.is_first(true);
+                index.with_general_delta(self.is_general_delta);
+                index.with_inline(self.is_inline);
+                index.with_version(self.version);
+            } else {
+                index.with_offset(self.offset);
+            }
+            self.index.push(index.build());
+            self.offset += data.len();
+            self.data.push(data);
+            self
+        }
+
+        pub fn build_inline(&self) -> Vec<u8> {
+            let mut bytes =
+                Vec::with_capacity(self.index.len() + self.data.len());
+            for (index, data) in self.index.iter().zip(self.data.iter()) {
+                bytes.extend(index);
+                bytes.extend(data);
+            }
+            bytes
+        }
+    }
+
+    #[test]
+    fn is_not_inline_when_no_inline_flag_test() {
+        let bytes = RevlogBuilder::new()
+            .with_general_delta(false)
+            .with_inline(false)
+            .push(IndexEntryBuilder::new(), vec![])
+            .build_inline();
+
+        assert_eq!(is_inline(&bytes), false)
+    }
+
+    #[test]
+    fn is_inline_when_inline_flag_test() {
+        let bytes = RevlogBuilder::new()
+            .with_general_delta(false)
+            .with_inline(true)
+            .push(IndexEntryBuilder::new(), vec![])
+            .build_inline();
+
+        assert_eq!(is_inline(&bytes), true)
+    }
+
+    #[test]
+    fn is_inline_when_inline_and_generaldelta_flags_test() {
+        let bytes = RevlogBuilder::new()
+            .with_general_delta(true)
+            .with_inline(true)
+            .push(IndexEntryBuilder::new(), vec![])
+            .build_inline();
+
+        assert_eq!(is_inline(&bytes), true)
+    }
+
+    #[test]
+    fn version_test() {
+        let bytes = RevlogBuilder::new()
+            .with_version(1)
+            .push(IndexEntryBuilder::new(), vec![])
+            .build_inline();
+
+        assert_eq!(version(&bytes), 1)
+    }
+}
diff --git a/rust/hg-core/src/revlog/patch.rs b/rust/hg-core/src/revlog/patch.rs
new file mode 100644
--- /dev/null
+++ b/rust/hg-core/src/revlog/patch.rs
@@ -0,0 +1,376 @@ 
+use byteorder::{BigEndian, ByteOrder};
+
+/// A chunk of data to insert, delete or replace in a patch
+///
+/// A chunk is:
+/// - an insertion when !data.is_empty() && start == end
+/// - an deletion when data.is_empty() && start != end
+/// - a replacement when !data.is_empty() && start > end
+/// - a noop when data.is_empty() && start == end
+#[derive(Debug, Clone)]
+struct PatchFrag<'a> {
+    start: i32,
+    end: i32,
+    data: &'a [u8],
+}
+
+impl<'a> PatchFrag<'a> {
+    /// Adjusted start of the chunk to replace.
+    ///
+    /// Offset allow to take into account the growth/shrinkage of data
+    /// induced by previously applied chunks.
+    ///
+    /// TODO This method should not exist.
+    ///      It its PatchList::combine responsibility.
+    fn start_offseted_by(&self, offset: i32) -> i32 {
+        self.start + offset
+    }
+
+    /// Adjusted end of the chunk to replace.
+    ///
+    /// Offset allow to take into account the growth/shrinkage of data
+    /// induced by previously applied chunks.
+    ///
+    /// TODO This method should not exist.
+    ///      It its PatchList::combine responsibility.
+    fn end_offseted_by(&self, offset: i32) -> i32 {
+        self.start_offseted_by(offset) + (self.data.len() as i32)
+    }
+
+    /// Length of the replaced chunk.
+    fn replaced_len(&self) -> i32 {
+        self.end - self.start
+    }
+
+    /// Length difference between the replacing data and the replaced data.
+    fn len_diff(&self) -> i32 {
+        (self.data.len() as i32) - self.replaced_len()
+    }
+}
+
+/// The delta between two revision data.
+#[derive(Debug, Clone)]
+pub struct PatchList<'a> {
+    /// A collection of chunks to apply.
+    ///
+    /// Those chunks are:
+    /// - ordered from the left-most replacement to the right-most replacement
+    /// - non-overlapping, meaning that two chucks can not change the same
+    ///   chunk of the patched data
+    frags: Vec<PatchFrag<'a>>,
+}
+
+impl<'a> PatchList<'a> {
+    /// Create a `PatchList` from bytes.
+    pub fn new(data: &'a [u8]) -> Self {
+        let mut frags = vec![];
+        let mut data = data;
+        while !data.is_empty() {
+            let start = BigEndian::read_i32(&data[0..]);
+            let end = BigEndian::read_i32(&data[4..]);
+            let len = BigEndian::read_i32(&data[8..]);
+            assert!(0 <= start && start <= end && len >= 0);
+            frags.push(PatchFrag {
+                start,
+                end,
+                data: &data[12..12 + (len as usize)],
+            });
+            data = &data[12 + (len as usize)..];
+        }
+        PatchList { frags }
+    }
+
+    /// Return the final length of data after patching
+    /// given its initial length .
+    fn size(&self, initial_size: i32) -> i32 {
+        let mut res = initial_size;
+        for m in self.frags.iter() {
+            res += m.len_diff()
+        }
+        res
+    }
+
+    /// Apply the patch to some data.
+    pub fn apply(&self, initial: &[u8]) -> Vec<u8> {
+        let mut last: usize = 0;
+        let mut vec =
+            Vec::with_capacity(self.size(initial.len() as i32) as usize);
+        for PatchFrag { start, end, data } in self.frags.iter() {
+            vec.extend(&initial[last..(*start as usize)]);
+            vec.extend(data.iter());
+            last = *end as usize;
+        }
+        vec.extend(&initial[last..]);
+        vec
+    }
+
+    /// Combines two patch lists into a single patch list.
+    ///
+    /// Applying consecutive patches can lead to waste of time and memory
+    /// as the changes introduced by one patch can be overridden by the next.
+    /// Combining patches optimizes the whole patching sequences.
+    fn combine(&mut self, other: &mut Self) -> Self {
+        let mut frags = vec![];
+
+        // Keep track of each growth/shrinkage resulting from applying a chunk
+        // in order to adjust the start/end of subsequent chunks.
+        let mut offset = 0i32;
+
+        // Keep track of the chunk of self.chunks to process.
+        let mut pos = 0;
+
+        // For each chunk of `other`, chunks of `self` are processed
+        // until they start after the end of the current chunk.
+        for PatchFrag { start, end, data } in other.frags.iter() {
+            // Add chunks of `self` that start before this chunk of `other`
+            // without overlap.
+            while pos < self.frags.len()
+                && self.frags[pos].end_offseted_by(offset) <= *start
+            {
+                let first = self.frags[pos].clone();
+                offset += first.len_diff();
+                frags.push(first);
+                pos += 1;
+            }
+
+            // The current chunk of `self` starts before this chunk of `other`
+            // with overlap.
+            // The left-most part of data is added as an insertion chunk.
+            // The right-most part data is kept in the chunk.
+            if pos < self.frags.len()
+                && self.frags[pos].start_offseted_by(offset) < *start
+            {
+                let first = &mut self.frags[pos];
+
+                // TODO explain the math //
+                let (data_left, data_right) = first.data.split_at(
+                    (*start - first.start_offseted_by(offset)) as usize,
+                );
+                let left = PatchFrag {
+                    start: first.start,
+                    end: first.start,
+                    data: data_left,
+                };
+
+                first.data = data_right;
+
+                offset += left.len_diff();
+
+                frags.push(left);
+
+                // There is no index incrementation because the right-most part
+                // needs further examination.
+            }
+
+            // At this point remaining chunks of `self` starts after
+            // the current chunk of `other`.
+
+            // start_offset will be used to adjust the start of the current
+            // chunk of `other`.
+            // Offset tracking continue with end_offset to adjust the end
+            // of the current chunk of `other`.
+            let mut next_offset = offset;
+
+            // Discard the chunks of `self` that are totally overridden
+            // by the current chunk of `other`
+            while pos < self.frags.len()
+                && self.frags[pos].end_offseted_by(next_offset) <= *end
+            {
+                let first = &self.frags[pos];
+                next_offset += first.len_diff();
+                pos += 1;
+            }
+
+            // Truncate the left-most part of chunk of `self` that overlaps
+            // the current chunk of `other`.
+            if pos < self.frags.len()
+                && self.frags[pos].start_offseted_by(next_offset) < *end
+            {
+                let first = &mut self.frags[pos];
+
+                // TODO explain the math ? //
+                let how_much_to_discard =
+                    *end - first.start_offseted_by(next_offset);
+
+                // TODO Find why only data is changed and not start. //
+                first.data = &first.data[(how_much_to_discard as usize)..];
+
+                next_offset += how_much_to_discard;
+            }
+
+            // Add the chunk of `other` with adjusted position.
+            // TODO explain the math ? //
+            frags.push(PatchFrag {
+                start: *start - offset,
+                end: *end - next_offset,
+                data,
+            });
+
+            // Go back to normal offset tracking for the next `o` chunk
+            offset = next_offset;
+        }
+
+        // Add remaining chunks of `self`.
+        for elt in &self.frags[pos..] {
+            frags.push(elt.clone());
+        }
+        PatchList { frags }
+    }
+}
+
+/// Combine a list of patch list into a single patch optimized patch list.
+pub fn fold_patch_lists<'a>(lists: &[PatchList<'a>]) -> PatchList<'a> {
+    if lists.len() <= 1 {
+        if lists.is_empty() {
+            PatchList { frags: vec![] }
+        } else {
+            lists[0].clone()
+        }
+    } else {
+        let (left, right) = lists.split_at(lists.len() / 2);
+        let mut left_res = fold_patch_lists(left);
+        let mut right_res = fold_patch_lists(right);
+        left_res.combine(&mut right_res)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    struct PatchDataBuilder {
+        data: Vec<u8>,
+    }
+
+    impl<'a> PatchDataBuilder {
+        pub fn new() -> Self {
+            Self { data: vec![] }
+        }
+
+        pub fn replace(
+            &mut self,
+            start: usize,
+            end: usize,
+            data: &[u8],
+        ) -> &mut Self {
+            assert!(start <= end);
+            self.data.extend(&(start as i32).to_be_bytes());
+            self.data.extend(&((end as i32).to_be_bytes()));
+            self.data.extend(&((data.len() as i32).to_be_bytes()));
+            self.data.extend(data.iter());
+            self
+        }
+
+        pub fn get(&'a mut self) -> &[u8] {
+            &self.data[..]
+        }
+    }
+
+    #[test]
+    fn test_ends_before() {
+        let data = vec![0u8, 0u8, 0u8];
+        let mut patch1_data = PatchDataBuilder::new();
+        patch1_data.replace(0, 1, &[1, 2]);
+        let mut patch1 = PatchList::new(patch1_data.get());
+
+        let mut patch2_data = PatchDataBuilder::new();
+        patch2_data.replace(2, 4, &[3, 4]);
+        let mut patch2 = PatchList::new(patch2_data.get());
+
+        let patch = patch1.combine(&mut patch2);
+
+        let result = patch.apply(&data);
+
+        assert_eq!(result, vec![1u8, 2, 3, 4]);
+    }
+
+    #[test]
+    fn test_starts_after() {
+        let data = vec![0u8, 0u8, 0u8];
+        let mut patch1_data = PatchDataBuilder::new();
+        patch1_data.replace(2, 3, &[3]);
+        let mut patch1 = PatchList::new(patch1_data.get());
+
+        let mut patch2_data = PatchDataBuilder::new();
+        patch2_data.replace(1, 2, &[1, 2]);
+        let mut patch2 = PatchList::new(patch2_data.get());
+
+        let patch = patch1.combine(&mut patch2);
+
+        let result = patch.apply(&data);
+
+        assert_eq!(result, vec![0u8, 1, 2, 3]);
+    }
+
+    #[test]
+    fn test_overridden() {
+        let data = vec![0u8, 0, 0];
+        let mut patch1_data = PatchDataBuilder::new();
+        patch1_data.replace(1, 2, &[3, 4]);
+        let mut patch1 = PatchList::new(patch1_data.get());
+
+        let mut patch2_data = PatchDataBuilder::new();
+        patch2_data.replace(1, 4, &[1, 2, 3]);
+        let mut patch2 = PatchList::new(patch2_data.get());
+
+        let patch = patch1.combine(&mut patch2);
+
+        let result = patch.apply(&data);
+
+        assert_eq!(result, vec![0u8, 1, 2, 3]);
+    }
+
+    #[test]
+    fn test_right_most_part_is_overridden() {
+        let data = vec![0u8, 0, 0];
+        let mut patch1_data = PatchDataBuilder::new();
+        patch1_data.replace(0, 1, &[1, 3]);
+        let mut patch1 = PatchList::new(patch1_data.get());
+
+        let mut patch2_data = PatchDataBuilder::new();
+        patch2_data.replace(1, 4, &[2, 3, 4]);
+        let mut patch2 = PatchList::new(patch2_data.get());
+
+        let patch = patch1.combine(&mut patch2);
+
+        let result = patch.apply(&data);
+
+        assert_eq!(result, vec![1u8, 2, 3, 4]);
+    }
+
+    #[test]
+    fn test_left_most_part_is_overridden() {
+        let data = vec![0u8, 0, 0];
+        let mut patch1_data = PatchDataBuilder::new();
+        patch1_data.replace(1, 3, &[1, 3, 4]);
+        let mut patch1 = PatchList::new(patch1_data.get());
+
+        let mut patch2_data = PatchDataBuilder::new();
+        patch2_data.replace(0, 2, &[1, 2]);
+        let mut patch2 = PatchList::new(patch2_data.get());
+
+        let patch = patch1.combine(&mut patch2);
+
+        let result = patch.apply(&data);
+
+        assert_eq!(result, vec![1u8, 2, 3, 4]);
+    }
+
+    #[test]
+    fn test_mid_is_overridden() {
+        let data = vec![0u8, 0, 0];
+        let mut patch1_data = PatchDataBuilder::new();
+        patch1_data.replace(0, 3, &[1, 3, 3, 4]);
+        let mut patch1 = PatchList::new(patch1_data.get());
+
+        let mut patch2_data = PatchDataBuilder::new();
+        patch2_data.replace(1, 3, &[2, 3]);
+        let mut patch2 = PatchList::new(patch2_data.get());
+
+        let patch = patch1.combine(&mut patch2);
+
+        let result = patch.apply(&data);
+
+        assert_eq!(result, vec![1u8, 2, 3, 4]);
+    }
+}
diff --git a/rust/hg-core/src/revlog/index.rs b/rust/hg-core/src/revlog/index.rs
new file mode 100644
--- /dev/null
+++ b/rust/hg-core/src/revlog/index.rs
@@ -0,0 +1,298 @@ 
+use crate::revlog::{Revision, NULL_REVISION};
+use byteorder::{BigEndian, ByteOrder};
+
+pub const INDEX_ENTRY_SIZE: usize = 64;
+
+/// A Revlog index
+#[derive(Debug)]
+pub struct Index<'a> {
+    bytes: &'a [u8],
+    /// Offsets of index block start.
+    /// Only needed when the index is interleaved with data.
+    offsets: Option<Vec<usize>>,
+}
+
+impl<'a> Index<'a> {
+    /// Create an index from bytes.
+    /// Calculate the start of each entry when is_inline is true.
+    pub fn new(bytes: &'a [u8], is_inline: bool) -> Self {
+        if is_inline {
+            let mut offset: usize = 0;
+            let mut offsets = Vec::new();
+
+            while (bytes.len() - offset) >= INDEX_ENTRY_SIZE {
+                offsets.push(offset);
+                let end = offset + INDEX_ENTRY_SIZE;
+                let entry = IndexEntry {
+                    bytes: &bytes[offset..end],
+                    offset_override: None,
+                };
+
+                offset += INDEX_ENTRY_SIZE + entry.compressed_len();
+            }
+
+            Self {
+                bytes,
+                offsets: Some(offsets),
+            }
+        } else {
+            Self {
+                bytes,
+                offsets: None,
+            }
+        }
+    }
+
+    /// Return then index entry corresponding to the given revision if it
+    /// exists.
+    pub fn get_entry(&self, rev: Revision) -> Option<IndexEntry> {
+        if rev == NULL_REVISION {
+            return None;
+        }
+        if let Some(offsets) = &self.offsets {
+            self.get_entry_inline(rev, offsets)
+        } else {
+            self.get_entry_separated(rev)
+        }
+    }
+
+    fn get_entry_inline(
+        &self,
+        rev: Revision,
+        offsets: &[usize],
+    ) -> Option<IndexEntry> {
+        let start = *offsets.get(rev as usize)?;
+        let end = start.checked_add(INDEX_ENTRY_SIZE)?;
+        let bytes = &self.bytes[start..end];
+
+        // See IndexEntry for an explanation of this override.
+        let offset_override = Some(end);
+
+        Some(IndexEntry {
+            bytes,
+            offset_override,
+        })
+    }
+
+    fn get_entry_separated(&self, rev: Revision) -> Option<IndexEntry> {
+        let max_rev = self.bytes.len() / INDEX_ENTRY_SIZE;
+        if rev as usize >= max_rev {
+            return None;
+        }
+        let start = rev as usize * INDEX_ENTRY_SIZE;
+        let end = start + INDEX_ENTRY_SIZE;
+        let bytes = &self.bytes[start..end];
+
+        // See IndexEntry for an explanation of this override.
+        let offset_override = match rev {
+            0 => Some(0),
+            _ => None,
+        };
+
+        Some(IndexEntry {
+            bytes,
+            offset_override,
+        })
+    }
+}
+
+#[derive(Debug)]
+pub struct IndexEntry<'a> {
+    bytes: &'a [u8],
+    /// Allows to override the offset value of the entry.
+    ///
+    /// For interleaved index and data, the offset stored in the index
+    /// correspond to the separated data offset.
+    /// It has to be overrided with the actual offset in the interleaved index
+    /// which is just afert the index block.
+    ///
+    /// For separated index and data, the offset stored in the first index
+    /// entry is mixed with the index headers.
+    /// It has to be overrided with 0.
+    offset_override: Option<usize>,
+}
+
+impl<'a> IndexEntry<'a> {
+    /// Return the offset of the data if not overrided by offset_override.
+    pub fn offset(&self) -> usize {
+        if let Some(offset) = self.offset_override {
+            offset
+        } else {
+            let bytes = [&[0; 2][..], &self.bytes[0..=5]].concat();
+            BigEndian::read_u64(&bytes[..]) as usize
+        }
+    }
+
+    /// Return the compressed length of the data.
+    pub fn compressed_len(&self) -> usize {
+        BigEndian::read_u32(&self.bytes[8..=11]) as usize
+    }
+
+    /// Return the uncompressed length of the data.
+    pub fn uncompressed_len(&self) -> usize {
+        BigEndian::read_u32(&self.bytes[12..=15]) as usize
+    }
+
+    /// Return the revision upon which the data has been derived.
+    pub fn base_revision(&self) -> Revision {
+        // TODO Maybe return an Option when base_revision == rev?
+        //      Requires to add rev to IndexEntry
+
+        BigEndian::read_i32(&self.bytes[16..])
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[cfg(test)]
+    #[derive(Debug, Copy, Clone)]
+    pub struct IndexEntryBuilder {
+        is_first: bool,
+        is_inline: bool,
+        is_general_delta: bool,
+        version: u16,
+        offset: usize,
+        compressed_len: usize,
+        uncompressed_len: usize,
+        base_revision: Revision,
+    }
+
+    #[cfg(test)]
+    impl IndexEntryBuilder {
+        pub fn new() -> Self {
+            Self {
+                is_first: false,
+                is_inline: false,
+                is_general_delta: true,
+                version: 2,
+                offset: 0,
+                compressed_len: 0,
+                uncompressed_len: 0,
+                base_revision: 0,
+            }
+        }
+
+        pub fn is_first(&mut self, value: bool) -> &mut Self {
+            self.is_first = value;
+            self
+        }
+
+        pub fn with_inline(&mut self, value: bool) -> &mut Self {
+            self.is_inline = value;
+            self
+        }
+
+        pub fn with_general_delta(&mut self, value: bool) -> &mut Self {
+            self.is_general_delta = value;
+            self
+        }
+
+        pub fn with_version(&mut self, value: u16) -> &mut Self {
+            self.version = value;
+            self
+        }
+
+        pub fn with_offset(&mut self, value: usize) -> &mut Self {
+            self.offset = value;
+            self
+        }
+
+        pub fn with_compressed_len(&mut self, value: usize) -> &mut Self {
+            self.compressed_len = value;
+            self
+        }
+
+        pub fn with_uncompressed_len(&mut self, value: usize) -> &mut Self {
+            self.uncompressed_len = value;
+            self
+        }
+
+        pub fn with_base_revision(&mut self, value: Revision) -> &mut Self {
+            self.base_revision = value;
+            self
+        }
+
+        pub fn build(&self) -> Vec<u8> {
+            let mut bytes = Vec::with_capacity(INDEX_ENTRY_SIZE);
+            if self.is_first {
+                bytes.extend(&match (self.is_general_delta, self.is_inline) {
+                    (false, false) => [0u8, 0],
+                    (false, true) => [0u8, 1],
+                    (true, false) => [0u8, 2],
+                    (true, true) => [0u8, 3],
+                });
+                bytes.extend(&self.version.to_be_bytes());
+                // Remaining offset bytes.
+                bytes.extend(&[0u8; 2]);
+            } else {
+                // Offset is only 6 bytes will usize is 8.
+                bytes.extend(&self.offset.to_be_bytes()[2..]);
+            }
+            bytes.extend(&[0u8; 2]); // Revision flags.
+            bytes.extend(&self.compressed_len.to_be_bytes()[4..]);
+            bytes.extend(&self.uncompressed_len.to_be_bytes()[4..]);
+            bytes.extend(&self.base_revision.to_be_bytes());
+            bytes
+        }
+    }
+
+    #[test]
+    fn test_offset() {
+        let bytes = IndexEntryBuilder::new().with_offset(1).build();
+        let entry = IndexEntry {
+            bytes: &bytes,
+            offset_override: None,
+        };
+
+        assert_eq!(entry.offset(), 1)
+    }
+
+    #[test]
+    fn test_with_overridden_offset() {
+        let bytes = IndexEntryBuilder::new().with_offset(1).build();
+        let entry = IndexEntry {
+            bytes: &bytes,
+            offset_override: Some(2),
+        };
+
+        assert_eq!(entry.offset(), 2)
+    }
+
+    #[test]
+    fn test_compressed_len() {
+        let bytes = IndexEntryBuilder::new().with_compressed_len(1).build();
+        let entry = IndexEntry {
+            bytes: &bytes,
+            offset_override: None,
+        };
+
+        assert_eq!(entry.compressed_len(), 1)
+    }
+
+    #[test]
+    fn test_uncompressed_len() {
+        let bytes = IndexEntryBuilder::new().with_uncompressed_len(1).build();
+        let entry = IndexEntry {
+            bytes: &bytes,
+            offset_override: None,
+        };
+
+        assert_eq!(entry.uncompressed_len(), 1)
+    }
+
+    #[test]
+    fn test_base_revision() {
+        let bytes = IndexEntryBuilder::new().with_base_revision(1).build();
+        let entry = IndexEntry {
+            bytes: &bytes,
+            offset_override: None,
+        };
+
+        assert_eq!(entry.base_revision(), 1)
+    }
+}
+
+#[cfg(test)]
+pub use tests::IndexEntryBuilder;
diff --git a/rust/hg-core/src/revlog.rs b/rust/hg-core/src/revlog.rs
--- a/rust/hg-core/src/revlog.rs
+++ b/rust/hg-core/src/revlog.rs
@@ -8,6 +8,9 @@ 
 pub mod node;
 pub mod nodemap;
 pub use node::{Node, NodeError, NodePrefix, NodePrefixRef};
+pub mod index;
+pub mod patch;
+pub mod revlog;
 
 /// Mercurial revision numbers
 ///
diff --git a/rust/hg-core/Cargo.toml b/rust/hg-core/Cargo.toml
--- a/rust/hg-core/Cargo.toml
+++ b/rust/hg-core/Cargo.toml
@@ -23,9 +23,11 @@ 
 crossbeam = "0.7.3"
 micro-timer = "0.3.0"
 log = "0.4.8"
+memmap = "0.7.0"
+flate2 = { version = "1.0.16", features = ["zlib"], default-features = false }
+zstd = "0.5.3"
 
 [dev-dependencies]
 clap = "*"
-memmap = "0.7.0"
 pretty_assertions = "0.6.1"
 tempfile = "3.1.0"
diff --git a/rust/Cargo.lock b/rust/Cargo.lock
--- a/rust/Cargo.lock
+++ b/rust/Cargo.lock
@@ -1,6 +1,11 @@ 
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
 [[package]]
+name = "adler"
+version = "0.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
 name = "aho-corasick"
 version = "0.7.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -42,6 +47,14 @@ 
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
+name = "cc"
+version = "1.0.58"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "jobserver 0.1.21 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "cfg-if"
 version = "0.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -92,6 +105,14 @@ 
 ]
 
 [[package]]
+name = "crc32fast"
+version = "1.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "crossbeam"
 version = "0.7.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -176,6 +197,18 @@ 
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
+name = "flate2"
+version = "1.0.16"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "cfg-if 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)",
+ "crc32fast 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.67 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libz-sys 1.0.25 (registry+https://github.com/rust-lang/crates.io-index)",
+ "miniz_oxide 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "getrandom"
 version = "0.1.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -186,6 +219,11 @@ 
 ]
 
 [[package]]
+name = "glob"
+version = "0.3.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
 name = "hermit-abi"
 version = "0.1.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -205,6 +243,7 @@ 
  "byteorder 1.3.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "clap 2.33.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "crossbeam 0.7.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "flate2 1.0.16 (registry+https://github.com/rust-lang/crates.io-index)",
  "hex 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -220,6 +259,7 @@ 
  "same-file 1.0.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "tempfile 3.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "twox-hash 1.5.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "zstd 0.5.3+zstd.1.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -234,6 +274,22 @@ 
 ]
 
 [[package]]
+name = "itertools"
+version = "0.9.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "either 1.5.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "jobserver"
+version = "0.1.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "libc 0.2.67 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "lazy_static"
 version = "1.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -244,6 +300,17 @@ 
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
+name = "libz-sys"
+version = "1.0.25"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "cc 1.0.58 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.67 (registry+https://github.com/rust-lang/crates.io-index)",
+ "pkg-config 0.3.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "vcpkg 0.2.10 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "log"
 version = "0.4.8"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -299,6 +366,14 @@ 
 ]
 
 [[package]]
+name = "miniz_oxide"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "adler 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "num-integer"
 version = "0.1.42"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -333,6 +408,11 @@ 
 ]
 
 [[package]]
+name = "pkg-config"
+version = "0.3.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
 name = "ppv-lite86"
 version = "0.2.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -613,6 +693,11 @@ 
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
+name = "vcpkg"
+version = "0.2.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+
+[[package]]
 name = "vec_map"
 version = "0.8.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -649,18 +734,49 @@ 
 version = "0.4.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
+[[package]]
+name = "zstd"
+version = "0.5.3+zstd.1.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "zstd-safe 2.0.5+zstd.1.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "zstd-safe"
+version = "2.0.5+zstd.1.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "libc 0.2.67 (registry+https://github.com/rust-lang/crates.io-index)",
+ "zstd-sys 1.4.17+zstd.1.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "zstd-sys"
+version = "1.4.17+zstd.1.4.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "cc 1.0.58 (registry+https://github.com/rust-lang/crates.io-index)",
+ "glob 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "itertools 0.9.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libc 0.2.67 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
 [metadata]
+"checksum adler 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "ee2a4ec343196209d6594e19543ae87a39f96d5534d7174822a3ad825dd6ed7e"
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